1. Field of the Invention
This invention relates to a compound bearing assembly for supporting a swing arm of a hard disc drive.
2. Description of the Prior Art
A prior art hard disc drive as shown in FIG. 2, comprises a magnetic disc 10 which is driven for rotation by a motor M, and a swing arm (or head arm) 12 carrying at the end thereof a magnetic head 11 for writing data in the disc 10 at a predetermined position thereof and reading out data from the disc 10 at a given position thereof.
The swing arm 12 has a stem rotatably supported by a compound bearing assembly which uses two ball bearing units. As shown in FIGS. 4(a) and 4(b), a prior art bearing assembly for supporting the swing arm comprises two ball bearing units A and B and a sleeve-like spacer C. These components of the bearing assembly are produced separately and supplied to the user, i.e., the hard disc drive manufacturer or the swing arm manufacturer, to be assembled on a shaft D.
In other words, with the conventional swing arm support bearing assembly, the user has to assemble the two ball bearing units on the shaft via the spacer. This poses the following problems.
(a) The shaft has to be sized in its production to the inner diameter of the inner race rings of the ball bearing units. In addition, its rigidity is subject to restrictions.
(b) The spacer which is a separate component from the two ball bearing units, should have highly accurate parallelism between and flatness of its opposite end finished surfaces.
(c) Since the spacer is only clampedly interposed between the outer race rings of the two ball bearing units, it is necessary for the user to implement a highly accurate assembly process so as to make the sleeve and the shaft coaxial to each other.
(d) For the above reasons, assembling of a prior art bearing by the user cannot be easily done.